Pressure transducer



June 9, 1964 w. B. PEGRAM 3,136,970

PRESSURE TRANSDUCER Filed Jan. 18, 1963 F/GTZ IN VENTOR WILL/AM B.PEG/PAM Big ATTO/i/VE) United States Patent 3,136,970 PRESSURETRANSDUCER William B. Pegram, Swarthmore, Pa., assignor to InternationalResistance Company, Philadelphia, Pa., a corporation of PennsylvaniaFiled Jan. 18, 1963, Ser. No. 252,326 4 Claims. (Cl. 33842) in general,pressure transducers comprise a pressure responsive means, such as abellows or diaphragm, a variable electrical component, such as avariable resistor or a differential transformer, and a mechanicallinkage between the pressure responsive means and the variableelectrical component. In the operation of such transducers, a variationin the pressure applied to the pressure responsive means moves thepressure responsive means so as to vary the setting of the variableelectrical component through the connecting linkage. The electricaloutput of the electrical component being a function of the pressureapplied to the transducer provides an indication of the pressure.

One problem in such transducers is that the linkage connection betweenthe pressure responsive means and the variable electrical componentoften includes one or more bearings or pivots which can become worn orbroken during the operation of the transducer. Such wear or breakagewill cause either complete disruption of the operation of thetransducer, or will induce in accuracies in the readout of thetransducer. To prevent this, it is desirable to provide a straight,direct drive connection between the pressure responsive means and thevariable electrical component. However, the transducers which haveheretofore used a straight, direct drive connection between the pressureresponsive means and the variable electrical components support thedrive connection in one or more bearings. Such bearings create africtional drag on the drive connection so that the output of theelectrical component is not always an accurate indication of thepressure applied to the transducer. Although frictionless bearings couldbe used, such bearings make the construction of the transducer morecomplex, and thereby increase thecost of the transducer;

It is an object of the present invention to provide a novel pressuretransducer utilizing a straight, direct drive connection between thepressure responsive means and the variable electrical component.

it is a further object of the present invention to provide a pressuretransducer having a frictionless straight, direct drive connectionbetween the pressure responsive means and the variable electricalcomponent.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in thedrawings a form which is presently preferred; it being understood,however, that this invention is not limitedto the precise arrangementsand instrumentalities shown.

FIGURE 1 is a longitudinal medial sectional elevational view of thepressure transducer of the present invention.

FIGURE 2 is a sectional plan view taken along line 2-2 of FIGURE 1.

FIGURE 3 is a perspective view ofthe variable electrical component ofthe pressure transducer of the present invention. i

In general, the pressure transducer of the present in vention comprisesa pressure responsive means including a slack diaphragm secured across acyinder and secured to a piston within the cylinder. The piston is of adiameter smaller than the diameter of the bore of the cylinder so thatthere is no friction between the piston and the cylinder. A straight rodis connected between the 3,136,970 Patented June 9, 1964 piston and themovable contact of the variable resistor. The movable contact is insliding engagement with a resistance element. Electrical terminals areprovided for the resistance element and the moving contact. A spring isconnected to the rod to provide a force against which the pressure beingmeasured must act. The spring is of a type which permits movement of therod only in a direction'along the axis of the rod. Since the springpermits only longitudinal movement of the rod, no bearings are necessaryto support the rod. Thus, there is provided a frictionless straight,direct drive between the pressure responsive means and the variableelectrical component of the transducer of the present invention.

Referring to the drawing, the pressure transducer of the presentinvention is generally designated as 10.

Transducer 10 comprises a flat, rectangular base plate 12 having a pairof mounting ears 14 extending from its ends. Each of the mounting ears14 has a hole 16 therethrough. A cylinder 18 is secured to the bottomsurface of the base plate 12 by bolts 20 and 22. A cylinderfcover 24 issecured to the bottom of the cylinder 18 by bolts 26. Cylinder cover 24has a bore 28 in its top surface which is of the same diameter and is inalignment with the bore 30 of the cylinder 18. An inlet passage .32 isprovided in the bottom surface of the cylinder cover 24, and isconnected to the bore 28 of the cylinder cover by an opening 34. Afitting 36 is secured within the inlet passage 32. The fitting 36 isadapted to be connected to a mating fitting on a pipe, tube, etc. topermit the transducer 10to be connected to the source of pressure to bemeasured.

A slack diaphragm 38 extends across the mating ends of the cylinder bore30 and cover bore 28 with the periphery of the diaphragm being clampedtightly between the mating ends of the cylinder 18 and the cover 24. Bya slack diaphragm it is meant a daiphragm of an impervious materialwhich has sufficient flexibility to permit it to be flexed by a minimumforce. A piston 40 is-provided within the cylinder bore 30, and isseated on top of the diaphragm 38. The piston 40 is of a diametersmaller than the diameter of the cylinder bore 30 so that the pistondoes not contact the wall of the cylinder bore. A connecting rod 42extends through the piston 40 and the diaphragm 38. A nut 44 is threadedon the bottom end of the connecting rod 42, and clamps the diaphragm 38to the piston 40. The connecting rod 42 extends upwardly along the axisof the cylinder bore 30, through a hole 46 in the base plate 12, andprojects beyond the top surface of the base plate. A spring member,generally designated as 48, is mounted over the base plate 12, and isconnected to the connecting rod 42 in a manner which will be explainedlater. Spring member 48 is of a type which will allow movement of theconnecting rod 42 along only the longitudinal axis of the connectingrod. A spacer sleeve 50 is provided around the connecting rod 42 betweenthe spring member 48 and the piston 40. The outer diameter of the spacersleeve 50 is smaller than the diameter of the hole 46 in the base plate12so that the spacer sleeve can pass freely through the hole 46. Aresistor contact member,

generally designated as 52, is mounted on the connecting rod 42 over thespring member 48. A nut 54 is threaded on the top end of the connectingrod 42. The nuts 44 and 54 clamp the diaphragm 38, piston 40, spacersleeve .50, spring member 48, and resistor contact member 52 tightlytogether on the connecting rod 42.

As shown in FIGURE 2, the spring member 48 is an E-shaped spring havinga pair of outer arms 56 and 58, and an inner arm 60 all connectedtogether at a base 62. As shown in FIGURE 1, the spring member 48 ismade up of a plurality of relatively thin, flat leaf springs 64 mountedin stacked relation, and secured together at the base 62 of the springmember by rivets 66. The widths V of the arms 56, 58 and 60 of thespring member 48 are such that the total stiffness of the outer two arms56 and 58 is equal to the stiffness of the inner arm 60.

The spring member 48 extends over and is substantially parallel to thebase plate 12. The connecting rod 42 extends through a hole 68 in thefree end of the inner arm 60 of the spring member 48. A supportingbracket 70 is mounted on the base plate 12 in a manner which will beexplained later, and has a pair of arms 72 and 74 extending over thefree ends of the outer arms 56 and 58 respectively of the spring member48. A separate spacer block 76 is provided bteween each of the bracketarms 72 and 74 and the top surfaces of the spring arms 56 and 58. Aseparate bolt 78 extends through each of the bracket arms '72 and 74,the spacer block 76 and the spring arms 56 and 58 so that the free endsof the spring arms 56 and 58 are secured to the supporting bracket 70.Thus, the ends of the outer arms 56 and 58 of the spring member 48 aresecured to the base plate 12, the end of the inner arm 60 of the springmember is secured to the connecting rod 42, and the base 62 of thespring member is free floating.

A resistor mounting block 80 is seated on the base plate 12 adjacentrebut spaced from the end of the inner arm 60 of the spring member 48. Aspacer member 82 is seated on the resistor mounting block 80, and thesupporting bracket 70 is seated on the spacer member The bolt extendsthrough the supporting bracket element 88 is secured to a face of thesupport plate 86.

Resistance element 88 comprises a base of an electrical insulatingmaterial having a resistance material on the surface thereof. Theresistance material may be a film of any well known resistance material,such as carbon, a metal, etc., coated on the surface of the base, or aresistance wire helically wound around and along the base as a core. Apair of terminals 90 of an electrical conductive metal aresecured to thesupport plate 86 with one end of the terminals electrically connected tothe opposite ends of the resistance element 88, and the other ends ofthe terminals projecting beyond an edge of the support plate 86. Acollector wire 92 of an electrically conductive metal is mounted on thesupport plate 86 spaced from and parallel to the resistance element 88.The collector wire 92 is provided with a terminal 94 at one end whichprojects beyond an edge of the support plate 86. The resistor 84 ismounted on the mounting block 80 with the longitudinal axis of theresistance element 88 being parallel to the longitudinal axis of theconnecting rod 42 (see FIGURE 1).

As shown in FIGURE 3, resistor contact member 52 comprises a plate 96 ofan electrically conductive metal having a pair of spaced, parallel arms98 and 100 projecting from an edge thereof. The contact plate 96 isseated over the inner arm 60 of the spring member 48 with the connectingrod 42 extending through a hole 102 in the contact plate. The contactarms 98 and 100 project from the contact plate 96 beyond and across theend of the inner arm 60 of the spring member 48. The free end of thecontact arm 98 slidably engages the resistance element 88, and the freeend of the contact arm 100 slidably engages the collector wire 92.Contact member 52 is electrically insulated from the spring member 48and the connecting rod 42 by a pair of insulating washers 104 onopposite sides of the contact plate 96, .and an insulating sleeve 186extending around the connecting rod 42 and through the hole 102 in thecontact plate.

A terminal plug 108 extends through and is secured to the base plate 12.Terminal plug 108 is provided with three terminal pins or sockets 110which are insulated from each other and from the base plate 12. Each ofthe resistor element terminals is electrically connected to a separateone of the terminal pins by a separate wire 112. The collector terminal94 of resistor 84 is electrically connected to the third terminal pin110 by a wire 114.

A protective cover 116 is provided over the spring member 48, resistor84, and their supporting elements. The cover 116 is secured to the baseplate 12 by screws 118 extending through mounting ears 120 and threadedinto holes in the base plate.

In the use of the transducer 10 of the present invention, the transduceris connected to the source of pressure to be measured by means of apipe, tube or the like connected to the fitting 36. Thus, the pressureto be measured is applied to the bottom of the piston 40 through thediaphragm 38. As the pressure to be measured varies the piston 40 willbe moved longitudinally in the cylinder 18. Increases in the pressure tobe measured will move the piston 40 upwardly against the stiffness ofthe spring member 48, and decreases in the pressure will move the piston40 downwardly under the action of the spring 'member- Movement of thepiston 40 moves the contact member 52 through the connecting rod 42.Thus, variations in the pressure to be measured varies the position ofthe point of contact between the contact arm'90 and the resistanceelement 88 so as to vary the electrical output of the resistor 86. Theelectrical output of the resistor 86 can be measured by suitableinstrumentation connected to the terminals 110. By pre-calibrating theresistor 86, the pressure being measured can be directly determined bythe instrumentation connected to the transducer 10.

As previously stated, the spring member 48 is of a type which permitsmovement of the connecting rod 42 only longitudinally of the axis of theconnecting rod. Thus, the connecting rod 42 has no supporting bearingsso that there is no frictional drag on the movement of the connectingrod. Therefore, the electrical output of the transducer 10 provides anaccurate indication of the pressure being measured. Also, the connectingrod 42 provides a straight, direct connection between the piston 40 andthe resistor contact member 52 so that there is no linkage or linkagebearings to become worn or broken during the operation of the transducer10. Therefore,

.the transducer 10 of the present invention will have a long operatinglife.

The present invention may be embodied in other specific forms withoutdeparting from the spiritor essential attributes thereof, and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification as indicating the scope of theinvention.

I claim:

1. A pressure transducer comprising a flat base plate, a cylindersecured to one side of said base plate, said cylinder having a bore thelongitudinal axis of which is perpendicular to said base plate, a slackdiaphragm secured to said cylinder and extending across said cylinderbore, a piston seated against said diaphragm, the outer diameter of saidpiston being smaller than the diameter of the cylinder bore, a straightconnecting rod secured to the diaphragm and piston, said connecting rodextending through said cylinder bore and projecting through an openingin said base plate, an electrical resistor mounted on the other side ofsaid base plate, said resistor having a straight resistance elementextending parallel to said connecting rod and a pair of terminalselectrically connected to opposite ends of the resistance element, aresistor contact member mounted on said connecting rod and slidablyengaging said resistance element, a terminal electrically connected tosaid contact member, an E- shaped spring mounted over and extendingsubstantially parallel to the outer side of the base plate, the innerarm of said spring being secured to the connecting rod and the outerarms of the spring being secured to the base plate, said springpermitting movement of said connecting rod only longitudinally of theaxis of the connecting rod, and means for applying the pressure to bemeasured to said diaphragm and said piston.

2. A pressure transducer in accordance with claim 1 in which theresistor includes a collector member of an electrically conductive metalmounted parallel to the resistance element, and the contact memberincludes a pair of contact arms, one of said contact arms slidablyengaging the resistance element and the other contact arm slidablyengaging the collector member.

3. A pressure transducer in accordance with claim 1 in which the springmeans comprises a plurality of stacked E-shaped springs extendingsubstantially parallel to the base plate, the arms and the bases of saidsprings being rigidly secured together, the inner arms of said springsbeing secured to the connecting rod and the outer arms of the springsbeing securedto the base plate.

4. A pressure transducer in accordance with claim 3 in which thestiffness of the inner arms of the springs is equal to the totalstiffness of the outer two arms of the springs. t

References Cited in the file of'this patent UNITED STATES PATENTS2,649,294 Walter Aug. 18, 1953 2,976,734 Gindes et al. Mar. 28, 19612,989,063 Clark June 20, 1961 2,989,991 Knobel June 27, 1961 2,998,587Bourns et a1. Aug. 29, 1961 3,069,645 Henke Dec. 18, 1962

1. A PRESSURE TRANSDUCER COMPRISING A FLAT BASE PLATE, A CYLINDERSECURED TO ONE SIDE OF SAID BASE PLATE, SAID CYLINDER HAVING A BORE THELONGITUDINAL AXIS OF WHICH IS PERPENDICULAR TO SAID BASE PLATE, A SLACKDIAPHRAGM SECURED TO SAID CYLINDER AND EXTENDING ACROSS SAID CYLINDERBORE, A PISTON SEATED AGAINST SAID DIAPHRAGM, THE OUTER DIAMETER OF SAIDPISTON BEING SMALLER THAN THE DIAMETER OF THE CYLINDER BORE, A STRAIGHTCONNECTING ROD SECURED TO THE DIAPHRAGM AND PISTON, SAID CONNECTING RODEXTENDING THROUGH SAID CYLINDER BORE AND PROJECTING THROUGH AN OPENINGIN SAID BASE PLATE, AN ELECTRICAL RESISTOR MOUNTED ON THE OTHER SIDE OFSAID BASE PLATE, SAID RESISTOR HAVING A STRAIGHT RESISTANCE ELEMENTEXTENDING PARALLEL TO SAID CONNECTING ROD AND A PAIR OF TERMINALSELECTRICALLY CONNECTED TO OPPOSITE ENDS OF THE RESISTANCE ELEMENT, ARESISTOR CONTACT MEMBER MOUNTED ON SAID CONNECTING ROD AND SLIDABLYENGAGING SAID RESISTANCE ELEMENT, A TERMINAL ELECTRICALLY CONNECTED TOSAID CONTACT MEMBER, AN ESHAPED SPRING MOUNTED OVER AND EXTENDINGSUBSTANTIALLY PARALLEL TO THE OUTER SIDE OF THE BASE PLATE, THE INNERARM OF SAID SPRING BEING SECURED TO THE CONNECTING ROD AND THE OUTERARMS OF THE SPRING BEING SECURED TO THE BASE PLATE, SAID SPRINGPERMITTING MOVEMENT OF SAID CONNECTING ROD ONLY LONGITUDINALLY OF THEAXIS OF THE CONNECTING ROD, AND MEANS FOR APPLYING THE PRESSURE TO BEMEASURED TO SAID DIAPHRAGM AND SAID PISTON.